Along the Primary Curve: Simultaneous Source and Lens Reconstruction of Bright Arcs in Cluster Lenses

Abstract

Gravitational lensing is the phenomenon arising when light rays are deflected by the mass between the source and the observer. Largely magnified and highly distorted images of background galaxies are formed by these angular deflections if the deflecting mass distribution and the background sources align. As the most massive gravitationally bound objects in the universe, galaxy clusters are places where such alignments are usually found. By carefully analyzing the images of lensed galaxies, one can measure the mass, both visible and invisible, along the line-of-sight. These measurements are crucial in investigating the nature of dark matter, which constitutes most of the mass within clusters. Existing lensing analysis methods typically forward model the multiple images of dozens of background galaxies lensed by the cluster. To make this forward modeling computationally tractable, these multiple images are reduced to a much smaller summary data vector, which includes the locations, magnifications, and distortions. Our work avoids this loss of information by forward modeling the data at pixel-level. We develop a parametric model for the angular deflections near the bright arcs that allows us to control the shape of the curve that gives the directions of the eigenvectors of the Jacobian of the lensing matrix. The bright and extended images often follow such curves. We apply our analysis method to the bright arcs in gravitational lenses SDSS J1110+6459 and SDSS J0004-0103. We present our lens and source reconstructions for each system. With the application of our new method to many other lensing systems, we anticipate significant improvement in lens modeling near the critical curve, which will provide higher precision mass reconstructions for the deflectors. High-precision lens models allow for more robust de-lensing, which aids the studies of various highly magnified sources.